The functions f and g are defined as follows:
\(f : x \mapsto x^2 - 2x, \quad x \in \mathbb{R},\)
\(g : x \mapsto 2x + 3, \quad x \in \mathbb{R}.\)
Show that the equation \(gf(x) = 0\) has no real solutions.
Solution
First, find the expression for \(gf(x)\):
\(gf(x) = g(f(x)) = g(x^2 - 2x) = 2(x^2 - 2x) + 3\).
Simplify the expression:
\(gf(x) = 2x^2 - 4x + 3\).
To find if there are real solutions, solve \(2x^2 - 4x + 3 = 0\).
Calculate the discriminant \(b^2 - 4ac\) for the quadratic equation \(ax^2 + bx + c = 0\):
Here, \(a = 2\), \(b = -4\), \(c = 3\).
\(b^2 - 4ac = (-4)^2 - 4 \times 2 \times 3 = 16 - 24 = -8\).
Since the discriminant is negative, the quadratic equation has no real solutions.
Therefore, the equation \(gf(x) = 0\) has no real solutions.
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